Human facial expressions are the best way of looking at how the limbic system works practically- wherever people are in the world, facial expressions mean the same thing. When we see another person in the population displaying a facial expression we often subconsciously process whether we should react to something they are reacting to.
The broca limbic region is the border.
Papez circuit was the first hypothesis about the limbic system. The cingulate gyrus receives and sends information to and from the neocortex. It then causes the hippocampus triggering, then the hypothalamus, and the anterior thalamic nuclei (ATN) feeds back in the cingulate gyrus. This circuit was hypothesised due to looking at lesions in areas. For example, ATN lesions led to spontaneous laughter or crying. Phineas Gage's orbitofrontal cortex destruction also led to the idea that pleasure was in this cortex.
One of the changes to papez circuit is that there is controversy over the hippocampal involvement. Instead, many hypothesise that the amygdala is much more involved than papez realised.
The amygdala is in the temporal lobe and has nuclei that are functionally grouped. Kluver and Bucy noted that when this area was absent in monkeys they had no fear response. This can be seen in Urbach-Wiethe disease where the patient cannot name facial expressions. Also, in temporal lobe epilepsy often people feel a sense of dread before a seizure. Fear has thus been linked to the amygdala.
When the basolateral amygdala is lesioned there is a decrease in affective aggression. When the corticomedial area is lesioned, there is an increase in predatory aggression. The amygdala projects to the hypothalamus. Thus, papez circuit has the addition of the amygdala- as seen!